System Sensor 5603 Heat Detector, 135F Fixed Temp, Single-Circuit

The System Sensor 5603 is a single-circuit, fixed-temperature mechanical heat detector designed for fire detection and property protection applications. Featuring a 135 F (57 C) non-resettable thermal sensor, normally open contacts, and UL-listed 25 x 25 ft protected spacing for 10-foot ceilings, it activates when ambient heat reaches its rated temperature. The detector includes a reversible mounting bracket, 14-22 AWG screw terminals, and an external activation indicator. Its fixed-temperature sensing element does not provide rate-of-rise detection and requires replacement after activation.

System Sensor 5603 135 F Fixed-Temperature Single-Circuit Mechanical Heat Detector

The System Sensor 5603 Mechanical Heat Detector provides fixed-temperature fire detection for property protection applications and locations where smoke detection is impractical or inappropriate. Part of the System Sensor 5600 Series, the detector features a single-circuit, normally open contact configuration with a 135 F (57 C) activation temperature. Its mechanical sensing element uses a fusible alloy to hold a spring-loaded contact in position until the surrounding temperature reaches the rated threshold. When the alloy melts, the spring mechanism closes the electrical circuit to signal a connected fire alarm control panel. The 5603 is a fixed-temperature-only detector without rate-of-rise sensing, distinguishing it from combination fixed-temperature and rate-of-rise models in the same series. Its thermal element is non-resettable, requiring detector replacement following heat activation.

The 5603 provides UL-listed protected spacing of 25 x 25 ft (7.62 x 7.62 m) on a 10-foot ceiling, with installation spacing adjusted according to NFPA 72 requirements and applicable ceiling conditions. Its electrical contact ratings support 6-125 VAC at 3 A, 6-28 VDC at 1 A, 125 VDC at 0.3 A, and 250 VDC at 0.1 A for resistive loads. The detector measures 4.57 inches (116 mm) in diameter and 1.69 inches (43 mm) in height with its mounting bracket and weighs approximately 6 oz (170 g). The specified maximum normal installation temperature is 100 F (38 C), while the operating humidity range extends from 5% to 95% relative humidity, non-condensing. Exterior markings identify the detector's fixed-temperature activation method with the designation FX and display its 135 F/57 C thermal rating.

The System Sensor 5603 supports surface-mounted and flush-mounted electrical back box installations through its reversible mounting bracket. Compatible mounting configurations include single-gang boxes, 3.5-inch octagonal boxes, 4-inch octagonal boxes, and 4-inch square boxes equipped with square-to-round plaster rings. Integrated SEMS screw terminals accommodate 14-22 AWG conductors, allowing connection to compatible fire alarm initiating device circuits. When the detector reaches its fixed-temperature threshold, an external circular heat collector releases from the housing to provide a visible indication of thermal activation. The normally open contact arrangement supports compatible conventional fire alarm control panels that monitor contact closure for alarm initiation. Installers must verify panel compatibility, circuit supervision requirements, and electrical ratings before connecting the detector.

The System Sensor 5603 fixed-temperature heat detector is suitable for property protection applications in utility rooms, mechanical spaces, storage areas, and other indoor environments where conditions make conventional smoke detection unsuitable. Its UL 521 listing and 135 F fixed-temperature classification support use in appropriately designed fire detection systems, subject to applicable codes and installation requirements. Unlike the System Sensor 5601P, which combines fixed-temperature and rate-of-rise detection, the 5603 responds only when its fixed-temperature element activates. The System Sensor 5623 provides a related dual-circuit configuration with the same 135 F activation rating, while the 5604 provides single-circuit detection at 194 F (90 C). The 5603 cannot be heat-tested or restored after activation because its fusible sensing element is non-resettable. Installation and maintenance must follow the manufacturer's instructions, NFPA 72, and local authority requirements, with smoke detectors provided where required for life-safety protection.